Hole pattern for gas turbine combustor

BACKGROUND OF THE INVENTION

This disclosure relates to a combustor for a gas turbine engine and, more particularly, to a hole pattern formed in inner and outer combustor liners.

Gas turbine engines, such as those used to power modern commercial and military aircraft, include a compressor for pressurizing a supply of air, a combustor for burning a hydrocarbon fuel in the presence of the pressurized air, and a turbine for extracting energy from the resultant combustion gases. The combustor generally includes radially spaced apart inner and outer liners that define an annular combustion chamber therebetween. Arrays of circumferentially distributed combustion air holes penetrate multiple axial locations along each liner to radially admit the pressurized air into the combustion chamber. A plurality of circumferentially distributed fuel injectors project into the forward end of the combustion chamber to supply the fuel for mixing with the pressurized air.

Combustion of the hydrocarbon fuel in the presence of pressurized air is know to produce a number of pollutants including nitrogen oxide (NO_X) emissions that are subjected to stringent controls by regulatory authorities, and thus are sought to be minimized as much as possible.

At least one known strategy for minimizing NO_Xemissions is referred to as rich burn, quick quench, lean burn (RQL) combustion. The RQL strategy recognizes that the conditions for NO_Xformation are most favorable at elevated combustion flame temperatures, such as when a fuel-air ratio is at or near stoichiometric, for example. A combustor configured for RQL combustion includes three serially arranged combustion zones: a rich burn zone at the forward end of the combustor, a quench or dilution zone axially aft of the rich burn zone, and a lean burn zone axially aft of the quench zone.

During engine operation, a portion of the pressurized air discharged from the compressor enters the rich burn zone of the combustion chamber. Concurrently, the fuel injectors introduce a stoichiometrically excessive quantity of fuel into the rich burn zone. Although the resulting stoichiometrically fuel rich fuel-air mixture is ignited and burned to partially release the energy content of the fuel NO_Xformation may still occur.

The fuel rich combustion products then enter the quench zone where jets of pressurized air radially enter through combustion air holes from the compressor enter to the quench zone of the combustion chamber. The pressurized air mixes with the combustion products to support further combustion of the fuel with air by progressively deriching the fuel rich combustion products as they flow axially through the quench zone and mix with the air. Initially, the fuel-air ratio of the combustion products changes from fuel rich to stoichiometric, causing an attendant rise in the combustion flame temperature. Since the quantity of NO_Xproduced in a given time interval is known to increase exponentially with flame temperature, substantial quantities of NO_Xmay be produced during the initial quench process. As the quenching continues, the fuel-air ratio of the combustion products changes from stoichiometric to fuel lean, causing an attendant reduction in the flame temperature. However, until the mixture is diluted to a fuel-air ratio substantially lower than stoichiometric, the flame temperature remains high enough to generate considerable quantities of NO_X.

Finally, the deriched combustion products from the quench zone flow axially into the lean burn zone. Additional pressurized air in this zone supports ongoing combustion to release energy from the fuel. The additional pressurized air in this zone also regulates the peak temperature and spatial temperature profile of the combustion products in attempts to reduce turbine exposure to excessive temperatures and excessive temperature gradients.

One known example pattern of combustion air holes in the inner and outer liners includes a series of holes that have two different sizes, i.e. a major hole and a minor hole. The pattern includes a major hole diameter and a minor hole diameter that alternate with each other. A minor hole on one of the inner and outer liners is radially aligned in a major hole of the other of the inner outer liners. This alternating pattern continues about a circumference of each of the inner and outer liners. While this pattern has been effective in reducing NO_Xemissions, still greater improvement is desired as environmental regulations become increasingly more strict with regard to such emissions.

SUMMARY OF THE INVENTION

A combustor for a turbine engine includes an outer liner and an inner liner circumscribed by the outer liner. The outer liner has a row of circumferentially distributed outer combustion air holes and the inner liner has a row of circumferentially distributed inner combustion air holes. The inner and outer liners each include at least a major air hole having a first air hole size, an intermediate air hole having a second air hole size, and a minor air hole having a third air hole size. The first, second, and third air hole sizes are all different from each other for a respective liner.

In one example, the intermediate air holes are larger than the minor air holes and smaller than the major air holes.

In one example, the intermediate air hole is positioned circumferentially between the major and minor air holes.

In one example, the outer liner includes an additional outer air hole and the inner liner includes an additional inner air hole to form a four hole pattern. The additional air holes each comprise one of a major air hole, an intermediate air hole, or a minor air hole.

In one example, the major air hole from the inner liner is at least partially aligned in a radial direction with one of the minor or intermediate air holes from the outer liner.

In one example, the row of circumferentially distributed outer combustion air holes are comprised of a plurality of first hole sets that are circumferentially spaced apart from each other. Each first hole set includes at least one major air hole, one intermediate air hole, and one minor air hole. In another example configuration, each first hole set includes the additional air hole. The row of circumferentially distributed inner combustion air holes are comprised of a plurality of second hole sets that are circumferentially spaced apart from each other. Each second hole set includes at least one major air hole, one intermediate air hole, and one minor air hole. In another example configuration, each second hole set includes the additional intermediate air hole.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.

<figref idrefs="DRAWINGS">FIG. 1</figref> is a cross-sectional side elevation view of a combustor.

<figref idrefs="DRAWINGS">FIG. 2</figref> is a view taken substantially in the direction <b>2</b>-<b>2</b> of <figref idrefs="DRAWINGS">FIG. 1</figref>.

<figref idrefs="DRAWINGS">FIG. 3A</figref> is an exploded, enlarged perspective view of a portion of the combustor shown in <figref idrefs="DRAWINGS">FIG. 1</figref>.

<figref idrefs="DRAWINGS">FIG. 3B</figref> is an enlarged side elevation view of a portion of the combustor shown in <figref idrefs="DRAWINGS">FIG. 1</figref>.

<figref idrefs="DRAWINGS">FIG. 4A</figref> is a schematic representation of one example hole pattern.

<figref idrefs="DRAWINGS">FIG. 4B</figref> is a schematic representative of another example hole pattern.

<figref idrefs="DRAWINGS">FIG. 5A</figref> is a perspective schematic representation of inner and outer liners with one example of a hole pattern.

<figref idrefs="DRAWINGS">FIG. 5B</figref> is a schematic comparison of radially aligned holes from <figref idrefs="DRAWINGS">FIG. 5A</figref>.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A gas turbine engine includes a compressor (not shown), a diffuser <b>12</b> (partially shown), a combustor module <b>14</b>, and a turbine module <b>16</b> (partially shown). The combustor module <b>14</b> comprises a radially inner case <b>18</b> and a radially outer case <b>20</b>, concentric with the radially inner case <b>18</b>. The radially inner <b>18</b> and outer <b>20</b> cases circumscribe an axially extending engine centerline <b>22</b> to define an annular pressure vessel <b>24</b>. The combustor module <b>14</b> also includes a combustor <b>26</b> residing within the annular pressure vessel <b>24</b>. The combustor <b>26</b> includes a liner assembly comprising a radially inner liner <b>32</b> and a radially outer liner <b>34</b> that circumscribes the radially inner liner <b>32</b> to define an annular combustion chamber <b>36</b>. The inner <b>32</b> and outer <b>34</b> liners cooperate with the inner <b>18</b> and outer <b>20</b> cases to define respective inner <b>40</b> and outer <b>42</b> air plenums.

In the example shown, the outer liner <b>34</b> comprises a single piece outer support shell <b>44</b> connected to the outer case <b>20</b>, and forward and aft outer heatshields <b>46</b>, <b>48</b> secured by fasteners <b>54</b> to respective forward <b>50</b> and aft <b>52</b> portions of the outer support shell <b>44</b>. As seen best in the example of <figref idrefs="DRAWINGS">FIG. 2</figref>, each outer heatshield <b>46</b>, <b>48</b> comprises nine arcuate heatshield panels, such as representative panels <b>46</b><i>a </i>which each define an arc segment.

Similarly, the inner liner <b>32</b> comprises a single piece inner support shell <b>58</b> connected to the inner case <b>18</b>, and forward <b>60</b> and aft <b>62</b> inner heatshields are secured by fasteners <b>68</b> to respective forward and aft portions <b>64</b>, <b>66</b> of the inner support shell <b>58</b>. As seen best in <figref idrefs="DRAWINGS">FIG. 2</figref> each inner heatshield <b>60</b>, <b>62</b> comprises nine arcuate heatshield panels, such as panels <b>60</b><i>a </i>which each define an arc segment. Each inner and outer heatshield can subtend an arc of approximately 20-45 degrees. The radial separation between each shell and its respective heatshield panels is slightly exaggerated in <figref idrefs="DRAWINGS">FIG. 2</figref> for clarity purposes.

A plurality of axially and circumferentially distributed cooling air holes perforates the inner and outer liners. These cooling air holes, which are depicted only in <figref idrefs="DRAWINGS">FIGS. 3A and 3B</figref>, include a plurality of impingement cooling holes <b>70</b> penetrating transversely through the outer <b>44</b> and inner <b>58</b> support shells, and a plurality of film cooling holes <b>72</b> penetrating obliquely through the heatshields <b>46</b>, <b>48</b>, <b>60</b>, <b>62</b>. The cooling air holes <b>70</b>, <b>72</b> are readily distinguishable from combustion air holes described hereinafter because the cooling air holes <b>70</b>, <b>72</b> are far more numerous and substantially smaller than the combustion air holes. For example, the combustor <b>26</b> has a total of approximately 23,000 impingement holes, each about 0.64 millimeters (0.025 inches) in diameter, and a total of approximately 46,000 film cooling holes, each about 0.64 millimeters (0.025 inches) in diameter in the combustor <b>26</b> that includes thirty-six heatshield panels. Moreover, as described below, the cooling air discharged through the film cooling holes <b>72</b> hugs the heatshield panels to form a cooling film rather than penetrating into the interior of the combustion chamber <b>36</b> and participating in the combustion process.

During engine operation, pressurized cooling air from the plenums <b>40</b>, <b>42</b> enters the impingement cooling holes <b>70</b>. The cooling air exits the impingement cooling holes <b>70</b> as a first series of discrete jets that impinge on and cool the heatshields <b>46</b>, <b>48</b>. The impinged cooling air then flows through the film cooling holes <b>72</b>, which discharge a second series of cooling air jets into the combustion chamber <b>36</b>. Because the film cooling holes <b>72</b> are obliquely oriented, the second cooling air jets enter the combustion chamber <b>36</b> with a directional component that parallels the flame exposed surface of each heatshield. The parallelism helps the cooling air jets coalesce into a cooling film that hugs the flame exposed surfaces of the heatshields <b>46</b>, <b>48</b>. The illustrated film cooling holes <b>72</b> are oriented so that the cooling air discharged therefrom has both radial and axial directional components, however, the film cooling holes <b>72</b> may be oriented so that the discharged cooling air has a circumferential directional component as well. Additional disclosure regarding a similar shell and panel arrangement is contained in U.S. Pat. No. 5,758,503, the contents of which are incorporated herein by reference.

As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, the combustor <b>26</b> also includes a front end assembly <b>76</b> comprising an annularly extending hood <b>78</b>, a bulkhead assembly <b>80</b>, eighteen fuel injectors <b>82</b> and eighteen fuel injector guides <b>90</b> that each has a center opening <b>92</b>. The hood <b>78</b> extends radially between, and is secured to, the forwardmost ends of the inner and outer liners <b>32</b>, <b>34</b>. In this example, the hood <b>78</b> includes eighteen circumferentially distributed hood ports <b>84</b> that accommodate the fuel injectors <b>82</b> and introduce air into the forward end of the combustion chamber <b>36</b>. Each fuel injector <b>82</b> is secured to the outer case and projects through one of the hood ports <b>84</b> and through the central opening <b>92</b> in the corresponding fuel injector guide <b>90</b>. The front end assembly <b>76</b> is the exclusive vehicle for introducing primary combustion air into the forward end of the combustion chamber <b>36</b>. Additional disclosure regarding the structure of the bulkhead assembly, fuel injectors, air swirlers, and associated cooling passages is contained in U.S. Pat. No. 6,606,861, the contents of which are incorporated herein by reference.

As shown in <figref idrefs="DRAWINGS">FIGS. 1 and 2</figref>, the outer <b>34</b> and inner <b>32</b> liners each have a row <b>100</b>, <b>102</b> of circumferentially distributed combustion air admission holes penetrating therethrough. The outer row <b>100</b> of combustion air holes in the outer liner <b>34</b> is comprised of a set of collective patterns that are arranged in repeating order about a circumference of the outer liner. The pattern includes at least three combustion air holes, and in one example includes four combustion air holes. In one example, each pattern is aligned with one of the fuel injectors <b>82</b>, thus, the number of patterns through the liners is commensurate with the number of fuel nozzles.

When a three hole pattern is used, as shown in <figref idrefs="DRAWINGS">FIGS. 2 and 4A</figref>, the three combustion air holes have hole sizes that are different from each other. For example, the outer liner <b>34</b> includes a major air hole <b>104</b>, a minor air hole <b>106</b> that is smaller than the major air hole <b>104</b>, and an intermediate air hole <b>108</b> that is smaller than the major air hole <b>104</b> and larger than the minor air hole <b>106</b>.

The inner liner <b>32</b> in this example is similarly configured to include a major air hole <b>104</b>, a minor air hole <b>106</b> that is smaller than the major air hole <b>104</b>, and an intermediate air hole <b>108</b> that is smaller than the major air hole <b>104</b> and larger than the minor air hole <b>106</b>. The intermediate air holes <b>108</b> are positioned circumferentially between the major air holes <b>104</b> and the minor air holes <b>106</b>.

The outer row <b>100</b> of circumferentially distributed outer combustion air holes includes a plurality of first hole sets, with each first hole set comprising the three air hole pattern. Thus, each first hole set includes one minor air hole <b>106</b> that is circumferentially spaced from one intermediate air hole <b>108</b>, which is circumferentially spaced from one major air hole <b>104</b>. Each minor hole <b>106</b> of one first hole set is circumferentially spaced from a major air hole <b>104</b> of an immediately adjacent first hole set. Thus, the outer row <b>100</b> of circumferentially distributed outer combustion air holes has the pattern of one minor air hole <b>106</b>, followed by one intermediate air hole <b>108</b>, followed by one major air hole <b>104</b>, followed by one minor air hole <b>106</b>, followed by one intermediate air hole <b>108</b>, etc.

The inner row <b>102</b> of circumferentially distributed inner combustion air holes includes a plurality of second hole sets, with each second hole set comprising the three air hole pattern. The three hole pattern is similar to that described above and includes one minor air hole <b>106</b> that is circumferentially spaced from one intermediate air hole <b>108</b>, which is circumferentially spaced from one major air hole <b>104</b>. Each minor hole <b>106</b> of one second hole set is circumferentially spaced from a major air hole <b>104</b> of an immediately adjacent second hole set.

The air holes from the first hole set are at least partially radially aligned with some air holes from the second hole set. In the graphical example shown in <figref idrefs="DRAWINGS">FIG. 4A</figref>, a minor air hole <b>106</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned with a major air hole <b>104</b> from the second hole set of the inner row <b>102</b>. The intermediate air hole <b>108</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned with the intermediate air hole <b>108</b> from the second hole set for the inner row <b>102</b>. The major air hole <b>104</b> from the first hole set for the outer row <b>100</b> is at least partially radially aligned with the minor air hole <b>106</b> from the second hole set for the inner row <b>102</b>. A fuel nozzle position relative to the pattern is indicated at <b>110</b>. In the example shown, the fuel nozzle position <b>110</b> is generally aligned with the intermediate holes <b>108</b> of the three hole pattern.

In another example of a three hole pattern shown in <figref idrefs="DRAWINGS">FIG. 4B</figref>, the major air hole <b>104</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned with an intermediate air hole <b>108</b> from the second hole set of the inner row <b>102</b>. The intermediate air hole <b>108</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned with the major air hole <b>104</b> from the second hole set of the inner liner <b>102</b>. A minor air hole <b>106</b> from the first hole set of the outer row <b>100</b> is offset from a minor air hole <b>106</b> from the second hole set of the inner row <b>102</b>, with the intermediate <b>108</b> and major <b>104</b> air holes of the first and the second hole sets being positioned circumferentially between the minor air holes <b>106</b> of the first and the second hole sets. In other words, in this example, the minor air holes <b>106</b> are not radially aligned with each other, and are not radially aligned with the intermediate <b>108</b> or major <b>104</b> air holes. The fuel nozzle position <b>110</b> in this example is not aligned with any of the air holes but is positioned between the major <b>104</b> and intermediate <b>108</b> air holes of each of the first and second hole sets.

The holes in each of the rows <b>100</b>, <b>102</b> serve to regulate the quantity of combustion air admitted into the combustion chamber <b>36</b>. In the three hole pattern, the major air holes <b>104</b> are circumferentially positioned proximate to regions of strong swirl approaching the quench row. Placement of the intermediate <b>108</b>, <b>112</b> and minor <b>106</b> air holes in the outer <b>34</b> and inner <b>32</b> liners is managed and prescribed to impact the less prominent fuel/swirl regions while still promoting effective mixing of the pressurized air with the upstream fuel-air mixture and at pressurized air levels that secure the design intent and respective air flow requirements/restrictions. As air swirlers at the front end of the combustor impose a specific and distinct swirl (clockwise or counterclockwise), the patterns of the air holes in the inner <b>32</b> and outer <b>34</b> liners are mirror opposites, with the major air holes <b>104</b> positioned in the areas of strongest swirl proximate to the liner or in regions where the front end swirl drives flow towards the liner.

<figref idrefs="DRAWINGS">FIGS. 5A-5B</figref> show an example of a four hole pattern. The four hole pattern circumferentially repeats for both rows <b>100</b>, <b>102</b> in the manner described above with regard to the three hole pattern. The only difference is that there is an additional, i.e. a fourth combustion air hole. The fourth outer air hole includes an additional intermediate air hole <b>112</b> that is larger than the minor air holes <b>106</b> and smaller than the major air holes <b>104</b>. Thus, there are two intermediate air holes <b>108</b>, <b>112</b> in the four hole pattern. In the example shown, the intermediate air holes <b>108</b>, <b>112</b> have different sizes from each other; however, the intermediate air holes <b>108</b>, <b>112</b> could be of similar or equal sizes.

The intermediate air holes <b>108</b>, <b>112</b> are positioned circumferentially between the major air holes <b>104</b> and the minor air holes <b>106</b> in each of the rows <b>100</b>, <b>102</b>. As such, the outer row <b>100</b> of circumferentially distributed outer combustion air holes is comprised of a plurality of first hole sets. Each first hole set includes one minor air hole <b>106</b> that is circumferentially spaced from at least one of an intermediate air hole <b>108</b> and a major air hole <b>104</b>. The intermediate air holes <b>108</b>, <b>112</b> may be positioned adjacent to each other circumferentially between a major air hole <b>104</b> and a minor air hole <b>106</b> (see inner row <b>102</b> of <figref idrefs="DRAWINGS">FIG. 5B</figref>), or can be positioned on circumferentially opposing sides of a major air hole as shown for the outer row <b>100</b> in <figref idrefs="DRAWINGS">FIG. 5B</figref>. Each four hole pattern then repeats circumferentially about the inner and outer liners.

In this example, air holes from the first and second hole sets are also radially aligned in a pattern. As best shown in <figref idrefs="DRAWINGS">FIG. 5B</figref>, a minor air hole <b>106</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned with a major air hole <b>104</b> from the second hole set of the inner row <b>102</b>. One intermediate air hole <b>108</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned with one intermediate air hole <b>108</b> from the second hole set of the inner row <b>102</b>. A major air hole <b>104</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned another intermediate hole <b>112</b> from the second hole set of the inner row <b>102</b>. Another intermediate hole <b>112</b> from the first hole set of the outer row <b>100</b> is at least partially radially aligned with a minor air hole <b>106</b> of the second hole set of the inner row <b>102</b>.

The holes in each of the rows <b>100</b>, <b>102</b> serve to regulate the quantity of combustion air admitted into the combustion chamber <b>36</b>. In the four hole pattern, the major air holes <b>104</b> are circumferentially positioned proximate to fuel-rich regions or regions of strong swirl approaching the quench row. Placement of the intermediate <b>108</b>, <b>112</b> and minor <b>106</b> air holes in the outer <b>34</b> and inner <b>32</b> liners is managed and prescribed to impact the less prominent fuel/swirl regions while still promoting effective mixing of the pressurized air with the upstream fuel-air mixture and at pressurized air levels that secure the design intent and respective air flow requirements/restrictions. As the local fuel-air distributions and aerodynamics proximate to each liner vary, the patterns of the holes on the inner <b>32</b> and outer <b>34</b> liners specifically differ and need not be symmetric about a fuel nozzle centerline.

Each repeating pattern of air holes is each circumferentially aligned with one of the fuel injectors <b>82</b>, projections of which are designated <b>82</b>′ in <figref idrefs="DRAWINGS">FIG. 2</figref>, which shows a three hole pattern. The major air holes <b>104</b> are circular holes, each including a hole in the outer shell <b>44</b> and a corresponding hole in the forward outer heatshield <b>46</b>. As shown in <figref idrefs="DRAWINGS">FIG. 3A</figref>, a raised rim <b>120</b> that is integral with the heatshield <b>46</b>, circumscribes each major air hole <b>104</b> and occupies the radial space between the heatshield <b>46</b> and the outer shell <b>44</b> so that each major hole <b>104</b> is in the form of a short, sealed passage for conveying combustion air from the plenum <b>42</b> to the combustion chamber <b>36</b>. The major air holes <b>104</b> in the outer shell <b>44</b> are slightly larger than corresponding major air holes <b>104</b> in the heatshield <b>46</b> to account for manufacturing and assembly inaccuracies that might otherwise result in imperfect registration of the holes and attendant, undesirable restriction of fluid flow through the holes. Owing to their smaller size, any holes in a heatshield, rather than holes in the outer shell <b>44</b>, regulate the quantity of combustion air admitted into the combustion chamber <b>36</b>.

The outer liner <b>34</b> also includes minor air holes <b>106</b>, which in the example shown are circular holes, each including a hole in the outer shell <b>44</b> and a corresponding hole in the forward outer heatshield <b>46</b>. A raised rim <b>122</b>, integral with the heatshield <b>46</b>, circumscribes each minor air hole <b>106</b> and occupies the radial space between the heatshield <b>46</b> and the outer shell <b>44</b> so that each minor air hole <b>106</b> is in the form of a short, sealed passage for conveying combustion air from the plenum <b>42</b> to the combustion chamber <b>36</b>. Although not shown, the intermediate hole <b>108</b>, which would be positioned to the right of major air hole <b>104</b> when viewing <figref idrefs="DRAWINGS">FIG. 3A</figref>, would be similarly configured to have corresponding holes in the outer shell <b>44</b> and heatshield <b>46</b>, and would include a raised rim as described above. It should also be appreciated that the aft outer heatshield <b>48</b> also includes corresponding holes.

It should be appreciated that the inner row <b>102</b> of holes in the inner liner <b>32</b> would be similarly configured as those described above with regard to the outer row <b>100</b> of holes for the outer liner <b>34</b>. Examples of hole sizes are as follows: the minor air holes could be as small as 0.125 inches (3.18 mm) in diameter but in most examples would range within 0.250 inches (6.35 mm) to 0.300 inches (7.62 mm); the major air holes can be as large as 1.500 inches (38.1 mm) but in most examples would range within 0.600 inches (15.2 mm) to 0.750 inches (19.1 mm) in diameter; and the intermediate holes will fall somewhere between the major air hole sizes and minor air hole sizes depending upon specific applications.

It should be appreciated that the inner and outer hole diameters need not be of absolute or relative diameters as described in aforementioned sections. Other patterns of differing count or of a non-repeating nature could also be used. As known, fuel-air distributions and aerodynamics in combustors lack perfect repeatability. Moreover, front-end patterns in combustors may be mapped, simulated, or modeled. Therefore, it may be advantageous that the alignment with fuel nozzles, hole patterns, sizes and number on one liner or both liners, different other than that disclosed above.

The inner and outer rows <b>102</b>, <b>100</b> of combustion air holes are approximately axially aligned with each other and penetrate their respective liners <b>32</b>, <b>34</b> between 10% and 90% of the axial length L of the liner assembly. In the illustrated examples, each row <b>102</b>, <b>100</b> penetrates its respective liner at about midway along the axial length L of the liner assembly, which corresponds to a location proximate the leading edge of each aft heatshield <b>46</b>, <b>60</b>. The rows <b>100</b>, <b>102</b> of holes divide the combustion chamber into three combustion zones including a rich burn zone RB axially forward of the holes, a dilution or quench zone Q axially coincident with the holes, and a lean burn zone LB axially aft of the holes.

During engine operation, the diffuser <b>12</b> decelerates pressurized air flowing from the compressor. A first portion of the pressurized air enters the combustor <b>26</b> by way of the impingement and film cooling holes <b>70</b>, <b>72</b> to cool the heatshields <b>46</b>, <b>48</b>, <b>60</b>, <b>62</b> and by way of the cooling holes to cool the bulkhead assembly <b>80</b>. A second portion of the pressurized air enters the rich burn zone RB of the combustion chamber <b>36</b> by way of various passages in the front end assembly <b>76</b>. The pressurized air is referred to as primary combustion air because it intermixes with a stoichiometrically excessive quantity of fuel introduced through the fuel injectors <b>82</b> to support initial combustion in the rich burn zone RB. The rich stoichiometry of the fuel-air mixture in the rich burn zone produces a relatively cool flame, thus facilitates preventing excessive NO_Xformation and guarding against blowout of the combustion flame during any abrupt reduction in engine power. The front end assembly <b>76</b> is the dominant vehicle for introducing primary combustion air into the combustion chamber <b>36</b>. In comparison, introducing the primary air elsewhere, e.g. through combustion air openings in the forward end of the inner <b>32</b> and outer <b>34</b> liners, would provoke excessive NO_Xformation by producing stoichiometrically or nearly stoichiometrically proportioned pockets of fuel and air in the forward end of the combustion chamber.

The combustion products from the rich burn zone RB, which include unburned fuel, then enter the quench zone Q. A third portion of the pressurized air from the compressor flows from plenums <b>40</b>, <b>42</b> and into the quench zone Q through the rows <b>100</b>, <b>102</b> of combustion air holes. This third portion of pressurized air is referred to as dilution air because it facilitates diluting or deriching the combustion products from their stoichiometrically rich state at the forward edge of the quench zone Q to a stoichiometrically lean state at or just downstream of the aft edge of the quench zone Q. Intimately mixing dilution air with the combustion products flowing through the combustion chamber allows the fuel-air mixture to quickly become both thoroughly blended and regularly distributed. As used herein, the term “regular” refers to a state in which the fuel-air ratio is substantially uniform in the circumferential direction (at any arbitrarily specified radius) and in which the radial distribution of fuel-air ratio is either uniform or varies in a desired, pre-established way.

The air holes set forth in the described examples are specified as having different diameters and orientation to match the approaching flow and/or fuel-air mixture from the primary or rich burn zone RB and to optimize the quench process. The penetration depth of the dilution air and the corresponding quantity of pressurized air admitted through the holes may be regulated by specifying the relative sizes of the holes since the penetration depth of the jets and the fluid admission capacity of the holes both increase with increasing hole size. As a result, different combustion chamber designs are able to adjust to the temperature profile of the combustion gases by adjusting the size of the large holes, without compromising fuel-air mixing, which could lead to elevated levels of NO_X.

The combustion products from the quench zone Q then enter the lean burn zone LB where the combustion process concludes. As the combustion products flow into the lean burn zone LB, the air jets are not only swept downstream, but also continue to penetrate radially and spread out laterally and intermix thoroughly with the combustion gases. Evaluations using sophisticated computational fluid dynamics (CFD) techniques have shown the efficacy of the combustor.

Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.

The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.